1. Field of the Invention
The present invention relates to a power window device for an automotive vehicle, wherein a window glass is opened and closed by a drive source, e.g., a motor. More particularly, the invention relates to a power-window safety device which detects a state wherein a hand, head or the like of a person is caught between the window glass and the sash, wherein the power window device of the present invention carries out a safety control operation so as to prevent the window from closing in such a dangerous situation.
2. Related Art
In a general power window, the window glass is opened and closed by a motor. Accordingly, an accident wherein a hand, head or the like of a passenger is caught between the window glass and the sash, often occurs. A power-window safety device for protecting the passenger or the like against such an accident has been proposed. The proposed safety device detects a state wherein an object is caught between the window glass and the sash, and stops the closing operation of the window glass, or opens the window glass. More precisely, in the proposed safety device, a pulse generator including a Hall element is attached to the motor for driving the window glass. A speed detector detects a speed of the closing window glass by counting pulses output from the pulse generator. Further, the proposed safety device detects a direction of the moving window glassxe2x80x94either the closing or opening directionxe2x80x94and judges whether the window glass is in a safety control region where a safety operation should be carried out to prevent an object from being caught. The safety device detects when an object is caught, i.e., an object-caught state, on the basis of a change in the rate of the detected speed during the closing operation of the window. If the safety device detects that an object is caught, it executes a safety control operation wherein it forcibly moves the window glass in the opening direction to release the object from being caught in the window.
In the safety control region judgment technique, however, an unwanted situation may occur wherein the safety device mistakenly judges the safety control region due to an error in counting the pulses. This necessitates the following measure to reset the pulse counter: first, the window is set to its full open positionxe2x80x94because a full open position of the window glass is highly accurately detected by providing a window glass position detecting mechanism, such as a limit switch, near the upper limit of the window glassxe2x80x94and then a safety control region is set based on the full open position. In a specific example of the reset measure, position-sensors are disposed along a rail along which the window is moved for opening and closing. The position sensors"" resistance values, which vary with opening/closing positions of the window glass, are detected. The safety control region is then judged on the basis of the detected resistance values.
In the conventional safety device, which uses the pulse generator and the window glass position detecting mechanism, pulses output from the Hall element of the pulse generator are counted. Therefore, the conventional safety device cannot detect angular positions of the motor, or the window glass positions, at steps each shorter than the pulse width of the pulse signal output from the pulse generator. This makes it difficult to control the window glass position with high precision.
Further, to detect the safety control region, a window glass position detecting mechanism is needed in addition to the pulse generator. This leads to complexity in the construction of the whole device. The sash, which comes into contact with the window glass when the window is fully closed, is provided with a weather strip. The weather strip will be deformed when ambient conditions of temperature and the like vary. At this time, the full closing position of the window glass also shifts from its original position, and the safety control region also shifts from its original position. A mechanical means, like the window glass position detecting mechanism, which directly detects the window glass position, lacks the flexibility to detect such changes in ambient condition and, therefore, is unable to account for such a temperature variation.
Accordingly, an object of the present invention is to provide a power-window safety device which is advantageously includes a simplified construction, improved accuracy of detecting opening/closing positions of the window glass, and further includes the ability to account for a shift of the safety control region caused by a change in the ambient conditions.
To achieve the above and other objects, there is provided a power-window safety device which opens and closes a window glass of an automotive vehicle by use of a drive motor, and which carries out a safety control operationxe2x80x94to prevent an object from being caughtxe2x80x94by detecting an opening/closing position of the window glass. The safety device includes: an angular position sensor for detecting an angular position of the drive motor; position detecting means for detecting an opening/closing position of the window glass on the basis of an output signal of the angular position sensor; and safety control means for carrying out a safety control operationxe2x80x94to prevent an object from being caughtxe2x80x94in accordance with an output signal of the position detecting means. In the safety device, the angular position sensor includes a magnet mounted on a rotary output shaft of the motor, and a magnetic flux sensor. The magnetic flux sensor is disposed so as to face the magnet, and detects a variation of the magnetic flux from the magnet. The variation of the magnetic flux is caused by a rotation of the rotary output shaft, therefore an opening/closing position of the window glass is detected on the basis of a detect signal derived from the magnetic flux sensor. A reduction mechanism reduces the rotary output shaft""s rotational speed. The magnetic flux sensor preferably contains a plurality of Hall ICs which arc disposed at different angular positions around the rotary output shaft of the motor. Each of the Hall ICs processes a voltage output from its Hall element into a voltage which linearly varies in amplitude with respect to a rotational angle of the rotary output shaft. The position detecting means then detects an opening/closing position of the window glass on the basis of the voltage output from each Hall IC.
In the present invention, the angular position sensorxe2x80x94for detecting an angular position of the drive motor, which angular position has a correlation with an opening/closing position of the window glassxe2x80x94includes a magnet and a Hall IC detector. The magnet is mounted on a rotary output shaft of the motor for opening and closing the window glass. The Hall IC detector contains one or more Hall ICs for detecting a variation of the magnetic flux from the magnet, which change in magnetic flux is caused by a rotation of the rotary output shaft. Therefore, the safety device can detect a full stroke of the window movementxe2x80x94which ranges from a position where the window is fully opened to another position where the window is fully closedxe2x80x94by use of only the output signal of the Hall IC detector. This feature contributes to size reduction and circuit simplification, and makes the device easy to assemble into automotive vehicles. The opening/closing position of the window glass is detected by detecting an angular position of the rotary output shaft of the drive motor. With this unique feature, a change in rate of the output voltage with respect to the change in window position may be set at a large value. Further, the opening/closing position of the window glass is detected on the basis of the result from a process of linearly approximating the output voltage of the Hall element of the Hall IC detector. Therefore, a computing operation for determining window position is easy. Furthermore, there is no need for providing an additional mechanical detecting mechanism, such as the window glass position detecting mechanism. As a result, the safety device of the present invention can account for variations in the ambient conditions during its position detecting operation.